testutilsqemu: Introduce ARG_QEMU_CAPS_DEL, to mask out flags from real caps
In certain cases we want to use as-real capabilities as possible but
that doesn't allow testing certain fallback scenarios of features that
can be complied out of QEMU.
ARG_QEMU_CAPS_DEL can be used similarly to ARG_QEMU_CAPS but the flag
arguments are actually masked out of the resulting caps.
Signed-off-by: Peter Krempa <pkrempa@redhat.com> Reviewed-by: Ján Tomko <jtomko@redhat.com>